In an image-forming apparatus, a fixing device heats and presses a toner image that has been transferred to a transfer-receiving material such as paper or a synthetic resin sheet, thereby fixing the toner image on the transfer-receiving material. A rotary member such as a roller or a belt is used in this fixing. For example, heating is performed while a transfer-receiving material is caused to pass between a fixing roller and a pressure roller that is in contact with the fixing roller under pressure. Unfixed toner is thereby melted and fixed on the transfer-receiving material. The rotary member for a fixing device, such as a fixing roller or a fixing belt, or a pressure roller or a pressure belt, requires (1) a toner releasing property, (2) a thermal conductive property, and (3) durability.
In order to ensure these properties, a fluororesin layer is formed as an outermost layer of the rotary member for a fixing device. PTL 1 describes that a surface of a pressure belt obtained by using a thermosetting polyimide tube is covered with a heat-shrinkable tetrafluoroethylene/perfluoroalkylvinylether copolymer (PFA) tube to form a fluororesin layer.
Heat shrinkability is imparted to a fluororesin tube by stretching the tube at least in the radial direction. An example of a method for stretching a tube includes continuously feeding an unstretched tube in a stretching pipe, inflating the tube by applying an internal pressure to the tube, and bringing the inflated tube into contact with the inner wall of the stretching pipe to regulate the inflated diameter of the tube.